Funka Bay Research Articles

Annual variation in otolith increment widths of walleye pollock (Gadus chalcogrammus) larvae in Funka Bay, Hokkaido, Japan

AbstractTo clarify relationships between year‐class strength and larval growth of walleye pollock (Gadus chalcogrammus), and oceanographic conditions in the Pacific stock off Hokkaido and Tohoku, Japan, we undertook conductivity/temperature/depth (CTD) observations and investigated larval densities, larval otolith increment widths and larval prey densities (of copepod nauplii) of the 2008, 2009, 2010 and 2011 yr classes in Funka Bay. Oyashio Coastal Water (OCW) flowed into the bay in late February in 2008, 2010 and 2011, and the mean water temperatures decreased to 1.9–3.1 °C in March. OCW was not observed in 2009, and it was warm in late February (≥3.4 °C). Increment widths of lapillar otoliths during the yolk‐sac stage were wide in 2009 and 2011, medium in 2010 and narrow in 2008. Increment widths during the first‐feeding stage tended to become wider as the hatch month progressed, and the annual variation during the first‐feeding stage was larger than that of the yolk‐sac stage. The densities of the primary food for the larvae were high in 2008 when larval increment widths were narrowest, so the effect of prey abundance on larval growth appeared to be small. The ranking of the larval abundance in March was nearly coincident with that of the increment width during the larval stage. We, therefore, suggest that the larval growth rate is associated with the mortality rate and that the growth–mortality hypothesis may be applicable to walleye pollock in Funka Bay. Feeding success under warm water conditions may be an important factor that contributes towards high growth rates.

Effects of hypoxia on the feeding intensity and somatic condition of the blackfin flounder Glyptocephalus stelleri in Funka Bay, Japan

To clarify effects of hypoxia on feeding and somatic condition of blackfin flounder Glyptocephalus stelleri, we studied the temporal relationship between hypoxia and feeding intensity as well as the condition of this species in May and August 2006–2012. Hypoxia occurred near the seafloor in August between 2010 and 2012 but not in May. Population densities of gammarid amphipods Ampelisca brevicornis and Melita sp., the main prey items of blackfin flounder, were consistently low; however, the somatic condition and feeding intensity of blackfin flounder increased during hypoxia. Such an increase was not detected in May 2012 under non-hypoxic conditions. These facts imply that the hypoxia increased prey availability for blackfin flounder through the increased exposure of the gammarids over the sea floor, and, thus, resulted in improved body condition in August 2011 and 2012. Hypoxia positively would influence the somatic condition and feeding intensity of blackfin flounder in Funka Bay in August 2011 and 2012; however, the somatic condition during this period did not reach the levels recorded in 1983, suggesting that habitat quality for blackfin flounder in Funka Bay in 2011 and 2012 was worse than that in 1983.

Primary productivity and nitrogen assimilation with identifying the contribution of urea in Funka Bay, Japan

Primary production is supported by utilization of several forms of nitrogen (N), such as nitrate, ammonium, and urea. Nevertheless, only few studies have measured the concentration and uptake of urea despite its importance as a nitrogenous nutrient for phytoplankton. We measured primary productivity monthly at four depths within the euphotic zone using a clean technique and the 13C method by a 24 h in situ mooring incubation over a year in Funka Bay, a subarctic coastal area in Japan, to make better updated estimates (re-evaluation) of annual primary production. Nitrogenous (N) nutrient assimilation rates (nitrate, ammonium and urea) were also measured to elucidate the relative contributions of these nutrients to autotrophic production and to distinguish between new and regenerated production. The estimated annual primary production was 164 g C m−2, which was 40–60% higher than the previously reported values in the bay. Use of a clean technique and more frequent measurement during the spring bloom may have contributed to the higher rates. The production during the spring bloom was 56.5 g C m−2, accounting for 35% of the annual production. The maximum daily productivity occurred in the bloom at 1.4 g C m−2 d−1, which is one of the highest values among the world embayments. The annual primary production in the bay was classified as mesotrophic state based on the classification by Cloern et al. (2014). The assimilation rate of nitrate was maximal at 54 nmol N L−1 h−1 during the bloom. During the post-bloom periods with nitrate depleted conditions, assimilation rates of ammonium and urea increased and accounted for up to 85% of the total N assimilation. The assimilation rate of urea was almost comparable to that of ammonium throughout the year. Taking urea into account, the f-ratio ranged from 0.15 under the nitrate-depleted conditions to 0.8 under the spring bloom conditions. These ratios were overestimated by 50% and 10%, respectively, if urea uptake was eliminated. We provide a valuable data for the primary production dataset in the world's ecosystems, and show that urea plays an important role in supporting regenerated production during late spring and summer.

Impact of Oceanographic Environmental Shifts and Atmospheric Events on the Sustainable Development of Coastal Aquaculture: A Case Study of Kelp and Scallops in Southern Hokkaido, Japan

We provide an overview of selected recent operational applications of satellite remote sensing and marine Geographic Information Systems (GIS) procedures to the practice of sustainable aquaculture in southern Hokkaido, Japan, focusing mainly on kelp and scallop aquaculture. We also developed a suitable aquaculture site-selection model (SASSM) for suspension culture of Gagome (a kelp species) in the same region. Models for Japanese kelp and Gagome showed that the distributions of the most suitable areas for both species overlapped. Competition between kelps was especially marked along the coastline between Hakodate and Esan. In addition, we examined the impact of oceanographic environmental changes and atmospheric events on scallop and kelp aquaculture sites, demonstrating that variations in the coastal Oyashio Current and the Tsugaru Warm Current significantly influenced the growth and harvesting seasons of scallops and kelps in Funka Bay and other sections of southern Hokkaido. Because a strong El Niño event occurred in 2010, January of that year was extremely cold. The proportion of suitable areas for both scallops and kelps during their respective growing seasons contracted in 2010. Thus, shifts in oceanographic and atmospheric conditions should be incorporated into sustainability management planning for coastal scallop and kelp aquaculture in southern Hokkaido.

Hyperspectral optical discrimination of phytoplankton community structure in Funka Bay and its implications for ocean color remote sensing of diatoms

Identification of phytoplankton functional groups is key to understanding marine biogeochemical cycles. For more accurate understanding of phytoplankton community structure and its implications for ocean color remote sensing applications, we investigated seasonal changes in phytoplankton pigments with high-performance liquid chromatography (HPLC), hyperspectral absorption coefficients of detritus (ad(λ)), phytoplankton (aph(λ)), and colored dissolved organic matter (aCDOM(λ)), and hyperspectral aph(λ) derived from remote sensing reflectance (aph_Rrs-derived(λ)) in the coastal waters of Funka Bay from 2010 to 2012. Chlorophyll a (Chl a) concentrations measured by HPLC ranged from 0.29 to 8.6mgm−3. Phytoplankton community compositions, as estimated by chemotaxonomic analysis (CHEMTAX) based on HPLC phytoplankton pigments, showed a seasonal succession of diatoms, chlorophyll b-containing phytoplankton (chlorophytes and prasinophytes), and cyanobacteria. Additionally, to identify the dominant type of phytoplankton with an alternative technique to CHEMTAX analysis, we employed a derivative spectroscopy/similarity index (SI) approach for aph(λ) as an optical detection technique for discriminating between different types of phytoplankton. In particular for diatom-dominated stations, SI values relative to the second derivative spectra of aph(λ) of diatom cultures, isolated from our study region, were significantly higher than those for chlorophyll b-containing phytoplankton- and cyanobacteria-dominated stations. Furthermore, we found a strong relationship between the SI values calculated from the second derivative spectra and the composition of diatoms as estimated by CHEMTAX. These results suggest that the two different methods validated each other's performance and precision in estimating relative diatom abundance from bulk samples and that it is possible to optically discriminate the dominance of diatoms using derivative spectra of aph(λ). We extended this combination approach to hyperspectral aph_Rrs-derived(λ), using a quasi-analytical algorithm within 400–546nm range. We found a significant correlation between SI values obtained from the second derivative spectra of aph_Rrs-derived(λ)/aph_Rrs-derived(443) and the composition of diatoms derived by CHEMTAX, but it was not as high as for aph(λ) measured by filter-pad analysis. These results indicate that using hyperspectral optical data of aph(λ) and Rrs(λ) with derivative spectroscopy is potentially a promising approach to identify seasonal variability in the composition of diatoms in coastal waters. Furthermore, a hyperspectral approach in combination with CHEMTAX analysis as a reference for phytoplankton community structure has proven useful in improving our understanding of phytoplankton community structure in the coastal waters of Funka Bay.

Implications of marine environment change on Japanese scallop (Mizuhopecten yessoensis) aquaculture suitability: a comparative study in Funka and Mutsu Bays, Japan

The determination of the causes for the changes in marine environment in areas with similar oceanic climate forcing on most suitable sites for scallop aquaculture can help to ensure long-term sustainability of the coastal ecosystem. This study assessed aquaculture suitability sites using dominant indicators of marine ecological dynamics on Japanese scallop culture in Funka and Mutsu Bays, Japan as comparative examples. Data sources comprised of Moderate Resolution Imaging Spectroradiometer (MODIS), four dimensional-variational (4D-VAR) data assimilation system, Advanced Land Observing Satellite (ALOS), in situ and buoy measurements. The suitable sites were ranked on a scale of 1 (least suitable) to 8 (most suitable). In the most suitable sites in aquaculture operational areas, Funka Bay had a high proportion (51.1%) than Mutsu Bay (13.7%) for the best performed model. Peaks of aquaculture suitability scores were attributed to potential effects of currents. Extreme sea temperatures (>24°C) in summer 2010 were associated with low performance of the 2010 model in Mutsu Bay and mortality of scallops based on sea temperature-depth visualizations. Future global warming effects are likely to decrease the most suitable culture sites in Funka Bay and loss of similar areas in Mutsu Bay. Thus, change in marine environment influences scallop culture development. Such concepts could form scientific basis for aquaculture planning on designated system of larval distribution and stock management of cultured species to minimize mortality and economic losses.

The role of snowmelt runoff on the ocean environment and scallop production in Funka Bay, Japan

This study investigated the role of snowmelt runoff on water circulation, water mass formation, and the production of cultured scallop larvae, as a part of a land-sea linkage, by analyzing hydrological data in conjunction with nutrient data and by conducting sensitivity experiments based on a coupled land-sea model of Funka Bay, Japan, a typical semi-enclosed bay. A comparison between observed data and the simulated runoff showed that, using newly compiled datasets of nutrient concentrations in rivers and groundwater, the model was sufficiently accurate to estimate the terrestrial dissolved inorganic nitrogen (DIN) flux from the river and submarine groundwater discharges (SGDs). The average volume flux from the SGDs accounted for 26% of the riverine runoff flux. The DIN flux from SGDs accounted for a maximum of 40% of the total DIN loading to the bay before the snowmelt period. Sensitivity experiments using an ocean simulation indicated that the freshwater flux supplied by snowmelt runoff not only enhances clockwise circulations along with upwelling along the coast, but also modifies the distributions of wintertime water masses in the bay. However, the snowmelt runoff has little effect on larvae transport since wind forcing, rather than riverine buoyancy, dominates the circulation patterns. The annual density of scallop spat was highly correlated with snowmelt runoffs associated with high DIN concentrations, which suggested that riverine nutrients can increase the biomass of phytoplankton in near-shore seas and improve food availability for scallop spawners, resulting in increased egg production in March to April. Therefore, the nutrient flux from agricultural source areas through the large snowmelt runoff has an important role in larvae production. Land-sea linkages need to be identified to design sustainable and synergetic systems of aquaculture and agriculture for the integrated management of coastal regions.

Changes in abundances of Alexandrium tamarense resting cysts after the tsunami caused by the Great East Japan Earthquake in Funka Bay, Hokkaido, Japan

The 2011 Great East Japan Earthquake and the subsequent huge tsunami greatly affected both human activity and the coastal marine ecosystem along the Pacific coast of Japan. The tsunami also reached Funka Bay in northern Japan and caused serious damage to the scallop cultures there, and this tsunami was believed to have affected the coastal environments in the bay. Therefore, we investigated the changes in the spatial abundance and distribution of the toxic dinoflagellates Alexandrium tamarense cysts before the tsunami (August 2010) and after the tsunami (May 2011, August 2011, May 2012 and August 2012) in the bay. Further, monthly sampling was conducted after the tsunami to identify seasonal changes of Alexandrium catenella/tamarense cysts and vegetative cells. Significant increases were observed in the populations of A. catenella/tamarense cysts, comparing the abundances before the tsunami (in August 2010; 70±61cystsg−1 wet sediment) to those just after it (in May 2011; 108±84cystsg−1 wet sediment), and both A. tamarense bloom (a maximum density was 1.3×103cellsL−1) and PSP (Paralytic Shellfish Poisoning) toxin contamination of scallops (9.4 mouse unitg−1 was recorded) occurred in the bay. Seasonal sampling also revealed that the encystment of A. tamarense and the supply of the cysts to bottom sediments did not occur in the bay from September to April. These results strongly suggested that the mixing of the bottom sediments by the tsunami caused the accumulation of the toxic A. tamarense cysts in the surface of bottom sediment through the process of redeposition in Funka Bay. Moreover, this cyst deposition may have contributed to the toxic bloom formation as a seed population in the spring of 2011.

Improved growth of flathead flounder Hippoglossoides dubius in hypoxic waters in Funka Bay, Japan

To identify the factors that influence the growth rate of flathead flounder Hippoglossoides dubius in Funka Bay, Japan, we studied temporal changes in the growth of this species and its prey from 1989 to 2012. The lowest growth rate of H. dubius was recorded in the 1995 year-class, which had experienced severe hypoxia between 1995 and 1997. However, the highest growth rate was recorded in the 2007 year-class, which had experienced hypoxia between 2009 and 2011. In 2000 and 2001, small-sized flounder (<200 mm TL) from the 1995 year-class were feeding on mysidaceans, whereas those from other year-classes fed on small Ophiura spp. (<9 mm in disc diameter) in 2009, 2011, and 2012. Small Ophiura spp. were more abundant in 2007 and 2011 than in 2002 and 2003. Successful recruitment of Ophiura spp. took place between 2007 and 2011 and cohorts from these years could tolerate hypoxia. This suggests that food availability improved under hypoxic conditions, which led to improved growth in small flounders. Large flounders (≥200 mm TL) from all year-classes fed on prickleback fishes (Stichaeidae) and walleye pollock Gadus chalcogrammus juveniles. The growth of large flounders was enhanced by an increase in the abundance of Stichaeidae fishes and G. chalcogrammus juveniles.

The regional impacts of climate change on coastal environments and the aquaculture of Japanese scallops in northeast Asia: case studies from Dalian, China, and Funka Bay, Japan

Climate changes affect coastal environments and aquaculture, threatening food security and economic growth. Japanese scallop (Mizuhopecten yessoensis) culture is economically important for the coastal communities of Dalian, China, and Funka Bay, Japan. In this study, we combined satellite remote-sensing data, in situ observations, and a suitable aquaculture site selection model to explore the interactions between marine environments and climate variability over a recent 10-year period (2003–2012). Our selection of appropriate zones in these two Far Eastern regions and our analyses of climatic event (Arctic Oscillation (AO), winter East Asian monsoon (EAM), and El Niño/La Niña Southern Oscillation (ENSO)) and meteorological (precipitation, temperature, and wind) data allowed us to determine the impacts of climate change on regional coastal environments and prospects for scallop aquaculture. These analyses showed that AO and EAM strongly influenced the aquaculture areas on the Dalian coast through their effects on temperature during winter. We also determined that wind was the main driving force behind regional environmental changes during spring. Conversely, ocean conditions and suitable areas in Funka Bay changed rapidly relative to oceanic and atmospheric circulation. In Funka Bay, areas appropriate for scallop aquaculture and variations in chlorophyll-a concentration (which reflect the availability of algal food for scallops) were strongly correlated with ENSO, precipitation, and air temperature. These correlations demonstrate the influence of oceanic and atmospheric parameters on the productivity of scallop aquaculture in Funka Bay. Adaptation to oceanic and atmospheric changes should be considered when developing plans and management strategies for coastal scallop aquaculture in northeast Asia.

Effect of environmental factors and prey species on daytime and nighttime vertical distribution of juvenile walleye pollock in and around Funka Bay

We examined factors affecting the vertical distribution of juvenile walleye pollock during “the second critical period” (i.e. the transition period of prey size) in and around Funka Bay, Hokkaido, Japan. During the day, small juveniles (<30 mm) were distributed mainly in shallow, warm, and low-salinity water within the bay, whereas larger ones (≥30 mm) occurred in deeper, cold and saline water. During the night, the large juveniles migrated to shallower depths. Outside the bay, small- and large-sized juveniles were distributed in water masses of similar physical properties during the daytime, whereas during the nighttime, most of the juveniles moved to shallower depth, and some juveniles dived to deeper water mass. Dietary analysis revealed that large juveniles fed on large copepods (≥0.5 mm in body width) more than small juveniles did. The composition of zooplankton in our survey area showed that large-sized copepods often occurred in deeper saline water. From these results, there is a possibility that juvenile pollock inside and outside Funka Bay occupied different water masses preferable for each feeding advantage.

A preliminary study to understand the transport process for the eggs and larvae of Japanese Pacific walleye pollock Theragra chalcogramma using particle-tracking experiments based on a high-resolution ocean model

We developed a realistic 1/50° high-resolution ocean model capable of resolving submesoscale variability, and performed particle-tracking experiments based on this ocean model to identify elements that significantly affect the transport of the eggs and larvae of the Japanese Pacific walleye pollock Theragra chalcogramma into Funka Bay. The high-resolution model reproduced representative features of the oceanographic conditions of the main spawning area and season. A comparison of particle-tracking experiments performed under the passive transport condition based on high-resolution (1/50°) and low-resolution (1/10°) ocean models showed that high-resolution modeling is essential in order to realistically simulate the transport process. In this regard, however, the vertical motion of particles cannot be explained by the passive transport condition, as it leads to unrealistically deep sinking of particles in the simulation. Turning our attention to feasible non-passive transport conditions, we then incorporated the buoyancy motion of particles and conducted additional experiments that mainly differed in the particle density adopted. We clarified that buoyancy is an important factor in the retention of particles near the sea surface, and that the ratio of the particles that remain in Funka Bay to the number of particles released is sensitive to the vertical motions/positions of the particles, implying that it is necessary to model this vertical motion more accurately by incorporating more realistic biological processes or a statistical distribution into the particle-tracking model.

Improvement of an aquaculture site-selection model for Japanese kelp (Saccharinajaponica) in southern Hokkaido, Japan: an application for the impacts of climate events

Abstract Liu, Y., Saitoh, S-I., Radiarta, I. N., Isada, T., Hirawake, T., Mizuta, H., and Yasui, H. 2013. Improvement of an aquaculture site-selection model for Japanese kelp (Saccharinajaponica) in southern Hokkaido, Japan: an application for the impacts of climate events. – ICES Journal of Marine Science, 70: . Japanese kelp (Saccharinajaponica) is one of the most valuable cultured and harvested kelp species in Japan. In this study, we added a physical parameter, sea surface nitrate (SSN) estimated from satellite remote sensing data, to develop a suitable aquaculture site-selection model (SASSM) for hanging cultures of Japanese kelp in southern Hokkaido, Japan. The local algorithm to estimate SSN was developed using satellite measurements of sea surface temperature and chlorophyll-a. We found a high correlation between satellite- and ship-measured data (r2 = 0.87, RMSE = 1.39). Multi-criteria evaluation was adapted to the SASSM to rank sites on a scale of 1 (least suitable) to 8 (most suitable). We found that 64.4% of the areas were suitable (score above 7). Minamikayabe was identified as the most suitable area, and Funka Bay also contained potential aquaculture sites. In addition, we examined the impact of El Niño/La Niña–Southern Oscillation (ENSO) events on Japanese kelp aquaculture and site suitability from 2003–2010. During El Niño events, the number of suitable areas (scores 7 and 8) decreased significantly, indicating that climatic conditions should be considered for future development of marine aquaculture.

An integrated approach to the heat and water mass dynamics of a large bay: High-resolution simulations of Funka Bay, Japan

[1] Heat and water mass transports tagged by water type in a bay were investigated using daily outputs from a high-resolution land-sea coupled model. The modeled circulation and water property distribution were similar to those reported by observations. In this paper, the heat angle is introduced to accurately define the roles of the lateral heat flux (LF) into the bay and the net surface heat flux on temperature changes in the bay water. As a result, ocean phenomena in the bay can be categorized by using the heat angle in an intensive LF regime on short-period timescales and a gradual LF regime on intraseasonal timescales. Our close examination revealed that the velocity fields can be classified into three flow patterns: a twin vortex accompanied by positive LF, a clockwise flow with negative LF, and an anticlockwise flow with both LFs. These patterns occur in both intensive and gradual LF regimes. Intensive wind-driven LF forced by atmospheric disturbances was often observed from summer to autumn in 2008, accompanying the intrusion of southern subtropical Tsugaru warm water that was colder than the deep bay water (LF < 0) and subarctic Oyashio water that was warmer than the surface bay water (LF > 0), but both were hardly found in 2009. This thermal contrast affects the interannual difference in the stratification inherent in the bay. Our integrated analysis method is useful for prompt and robust understanding of the thermal and dynamic states in a bay based on ocean simulation data.

A Visualization Study of Vortices Extracted from the Tremendous Ocean Simulation Data: An Application in Funka Bay

A Visualization Study of Vortices Extracted from the Tremendous Ocean Simulation Data: An Application in Funka Bay

Bottom-Intensified Flow Appears at the Formation Stage of Surface Clockwise Circulation in Funka Bay in Early Summer

Bottom-Intensified Flow Appears at the Formation Stage of Surface Clockwise Circulation in Funka Bay in Early Summer

Seasonal Variations of Bromoform Distribution in the Funka Bay

2011年10月から2012年8月まで約2か月ごとに北海道噴火湾（内浦湾）で海洋観測を行った．海岸と沿岸，海盆域で海水を採取し揮発性有機ハロゲン化合物（ハロカーボン）の濃度をガスクロマトグラフ質量分析計にて測定した．海洋が主要起源と考えられているブロモホルムの濃度分布を捉え，同一水塊での濃度変化から起源推定を行った．植物プランクトンの大増殖が起こる3月から4月にかけて噴火湾海盆域では，ブロモホルムの濃度が約1.3倍になった（上昇率5 pmol L－1 month－1）．この上昇は植物プランクトンによるブロモホルム生産によるものと考えられた．海岸付近の大型藻類の成長が活発になる4月から8月は，海岸付近でブロモホルム濃度が急上昇してから高濃度域が湾全体に広がり，海盆域平均で濃度が約1.7倍になった（上昇率4 pmol L－1 month－1）．この上昇は大型藻類によるブロモホルム生産によるものと考えられた．噴火湾のブロモホルム濃度の変化は植物プランクトンと大型藻類の両方の影響を受けることが分かった．

Genetic stock structure of walleye pollock (Theragra chalcogramma) inferred by PCR–RFLP analysis of the mitochondrial DNA and SNP analysis of nuclear DNA

Walleye pollock, Theragra chalocogramma, is one of the most important species in the North Pacific and Bering Sea ecosystems. However genetic population structuring of walleye pollock is uncertain. In the present study, genetic variation of walleye pollock collected in several spawning areas ranging from the Japan Sea to the Gulf of Alaska was investigated by DNA analysis. Three regions of the spacer control region, the ND5 and ND6 region (ND complex), and the ND1 and 16S rRNA region (rDNA complex) were amplified using the polymerase chain reaction (PCR). Restriction fragment length polymorphism (RFLP) was conducted on these PCR products and composite haplotypes were calculated. Furthermore, several nuclear DNA regions (actin, Calmodulin, S7 ribosomal protein, creatin kinase, and SypI gene) were investigated to study the stock structure of walleye pollock. It was considered that Calmodulin gene was one of good genetic marker, therefore we conducted SNP analysis for Calmodulin gene by SnaPshot kits. In RFLP analyses, there were no area-specific fragment patterns in the three regions, control region, ND complex and rDNA complex of mtDNA. However compositions of the fragment patterns for the three digested sets, control region/HinfI, rDNA complex/MspI and ND complex/MspI indicated that there are significant differences between around the Japan (Sado–Funka Bay–Wakkanai–Rausu) and the Bering Sea (Western Bering Sea–Nabarin–Atka I.–Bogoslof I). Furthermore, in the case of haplotype frequency, composition showed also significant genetic difference between two areas. Moreover, in Calmodulin analyses, haplotype compositions were changing from western area to eastern area gradually and the results of AMOVA analysis showed that there are interesting differences between western Pacific, western Bering Sea, and eastern Bering Sea. Judging from these results, it was considered that there are three populations of walleye pollock in the Northern Ocean. However, area-specific pattern was not found in some populations in the Northern Ocean. Therefore, we suggested that these populations were related by weak gene flow, and the walleye pollock was formed with meta-population around the Japan and the Bering Sea.

Annual changes in macrobenthos abundance in Funka Bay, Japan

The temporal variation in macrobenthos abundance was studied in Funka Bay in the periods 2001–2004 and 2007–2010. Dissolved oxygen just above the sea floor of the basin was lower and ignition loss at the level of the sea floor was higher in 2007–2010 than in 2001–2004. Macrobenthic species were categorized into three groups: long-lived species, sedental polychaeta Notomastus latericeus, and short-lived species. Ignition loss was the most influential factor affecting macrobenthos abundance as this variable restricts the recruitment of macrobenthos. The abundance of both long-lived species and N. latericeus was lower between 2007 and 2010 than between 2001 and 2004. Supplementation of oxygen from outside the bay by the Tsugaru Warm Current may be an important factor impacting the increase in the abundance of long-lived species. The abundance of N. latericeus barely increased between 2007 and 2010, possibly because dissolved organic matter, which is their food item, may have become limited due to a narrow chink between sediments with eutrophication. The abundances of short-lived species did not differ between the periods 2001–2004 and 2007–2010 due to the organisms having a low tolerance to hypoxia. The current conditions in Funka Bay are on the verge of turning the bay into an azoic zone.

Viability of Alexandrium tamarense cysts in the sediment of Funka Bay, Hokkaido, Japan: Over a hundred year survival times for cysts

The abundance of Alexandrium tamarense cyst was investigated vertically in a sediment core in Funka Bay, Hokkaido, Japan. Germination experiments were conducted to estimate the germination ability of the cysts at different depth layers of the sediment. Molecular identification with loop-mediated isothermal amplification (LAMP) of A. tamarense cysts and core dating with 210Pb methods (CRS model) were performed. The results indicated A. tamarense has presented since at least 100 years in Funka Bay and intensive bloom started occurring in the early 1960s and has continued until the late 1980s. Cysts from shallow layers of the sediment core displayed greater viabilities than those from deeper layers. However, successful germination of A. tamarense cysts was observed even at the deepest layer, indicating the long-term survival ability (approximately 100 years), and this is the longest record for survival of resting cysts on this species at present. The abundance of viable cysts deposited during the past intensive bloom period was approximately 1.4 times higher than that of recently deposited cysts, suggesting that the cysts in the sub-surface dense layers could potentially function as seed populations in Funka Bay. Thus, dredging the sediment in Funka Bay may involve the risk for initiation of toxic blooms.